Group communications are becoming more important aspects of telecommunication networks, and the demand for such services will continue to increase. For instance, there are presently many different systems and networks that allow group communication. Public safety organizations are particularly interested in group communications and dedicated resources are being provided for these organizations. Businesses and even personal users also have a desire to use group communication. As a result a suite of protocols have already been developed for use in group communications. These protocols are used to control interactive communications sessions including data streams such as audio (voice), video, text messaging, and internet protocols, for example between, or to, users (also referred to herein as subscribers) in a communications network. Each subscriber is typically associated with a communications device (also referred to herein as a subscriber unit, access terminal, user equipment, and the like) that is used to connect to the communications network.
In practice, a dispatcher can set up a group call with a defined set of users. The group call consists of establishing a communication session. For example, a dispatcher can initiate a session by sending a page containing a list of all subscriber units of a particular group. Alternatively, the dispatcher can use a Group ID associated with that group instead of a list of individual members. For example, a dispatcher can initiate a session by sending a group page to a large number of subscriber units of a particular group by just using a Group ID in a single page for that group.
A subscriber unit that is paged to join the group call is required to respond to the page before being able to join the session. In particular, upon receipt of the page, the subscriber units associated with that group respond by performing private ranging using a randomly number that they generate for their individual access codes. Using random number access codes allows subscribers units to be individually identified. However, the actual number of random access codes is limited, and it may be that different subscriber units generate the same access code. Therefore, not only will there be ranging congestion from all the subscriber unit that are ranging within a short timeframe, there is a real possibility that there will be ranging access code collisions between identical codes, which could prevent some subscriber units from properly joining the group call session, which is not desirable for sensitive communications such as in the area of public safety.
One solution to this problem has been to pre-define a separate, dedicated code for each subscriber unit to use, within a page. However, this is difficult to implement in practice as this may result in an uneven loading across the Ranging Codes, and consequently unequal Ranging Code blocking probabilities across the subscriber devices. Additionally, this may be difficult to implement in practice as this may require additional bits in the page message to indicate which dedicated codes are being allocated for the group members to respond, and how many members are in the group (so that others who are not part of the group will know which codes they are not allowed to use). Additionally, with some other solutions there are additional inefficiencies when the members of a group can change, requiring a complete redefinition for all members of the group from the dispatcher every time there is a change in membership. Furthermore, dedicating codes to UEs within a group may also require the reserving of codes for the group members and every cell where group members may exist (e.g., across the paging area). This consumes additional capacity, reserving codes, which will not actually be used because that particular UE is in a different cell.
Another solution would be to separate ranging responses in time (and possibly as well in code). However, separation in time (or time and code) introduces delay to the channel setup time in the order of few quantum units, where the delay is proportional to the number of group members in a sector multiplied the delay for each. For large groups, these serialization delays can increase call setup times beyond what is acceptable for certain systems, especially public safety dispatch systems, while also reducing the instantaneous capacity in the sector.
Therefore, a need exists for a technique that reduces ranging congestion and collisions for group calls in a communication network.
Skilled artisans will appreciate that common but well-understood elements that are useful or necessary in a commercially feasible embodiment are typically not depicted or described in order to facilitate a less obstructed view of these various embodiments of the present invention.